Process for the preparation of perylene-3,4,9,10-tetracarboxydiimides in a coloristically valuable pigment form

Abstract

Brilliant and easily dispersible perylene-3,4,9,10-tetracarboxydiimide pigments of high color strength and N-alkyl derivatives thereof having 1 to 4 carbon atoms per alkyl group can be prepared by subjecting finely divided crude pigments to a treatment by means of a mixture of water and an organic solvent from the class of alcohols, ketones, carboxylic acids or carboxylic esters.

We claim: 
     
       1. Process for the preparation of brilliant and easily dispersible perylene-3,4,9,10-tetracarboxydiimides of high color strength and N-alkyl derivative thereof having 1 to 4 carbon atoms per alkyl group, characterized in that the crude pigments are first brought into a finely divided form by milling in the absence of organic solvents with or without the addition of salt, by kneading in the presence of salt or reprecipitation from sulphuric acid, and then, after removal of salt or sulphuric acid, subjected to a treatment by means of a mixture of water and an organic solvent selected from the group consisting of alcohols, aliphatic or cycloaliphatic ketones, carboxylic acids and carboxylic esters. 
     
     
       2. Process according to claim 1, characterized in that it is carried out at temperatures between 60° C. and 200° C. and, if appropriate, under elevated pressure. 
     
     
       3. Process according to claim 1, characterized in that mixtures of water and C 1  -C 4  -alkyl esters of aromatic carboxylic acids are used. 
     
     
       4. Process according to claim 1, characterized in that methyl benzoate or dimethyl phthalate is used. 
     
     
       5. Process according to claim 1, characterized in that the starting material of the solvent treatment is used in the form of a moist press cake. 
     
     
       6. Process according to claim 1, characterized in that the treatment is carried out with 0.1 to 100 parts by weight of organic solvent per part by weight of dry pigment. 
     
     
       7. Process according to claim 1, characterized in that the treatment medium contains 1 to 30 parts by weight of water per part by weight of dry pigment.